1. Field of Invention
This invention relates to maintenance stations for ink jet printing apparatus.
2. Description of Related Art
Ink jet printers have at least one printhead that directs droplets of ink towards a recording medium. Within the printhead, the ink may be contained in a plurality of channels. Energy pulses are used to expel the droplets of ink, as required, from orifices at the ends of the channels.
In a thermal ink jet printer, the energy pulses are usually produced by resistors. Each resistor is located in a respective one of the channels, and is individually addressable by current pulses to heat and vaporize ink in the channels. As a vapor bubble grows in any one of the channels, ink bulges from the channel orifice until the current pulse has ceased and the bubble begins to collapse. At that stage, the ink within the channel retracts and separates from the bulging ink to form a droplet moving in a direction away from the channel and towards the recording medium. The channel is then re-filled by capillary action, which in turn draws ink from a supply container. Operation of a thermal ink jet printer is described in, for example, U.S. Pat. No. 4,849,774.
A carriage-type thermal ink jet printer is described in U.S. Pat. No. 4,638,337. That printer has a plurality of printheads, each with its own ink tank cartridge, mounted on a reciprocating carriage. The channel orifices in each printhead are aligned perpendicular to the line of movement of the carriage. A swath of information is printed on the stationary recording medium as the carriage is moved in one direction. The recording medium is then stepped, perpendicular to the line of carriage movement, by a distance equal to the width of the printed swath. The carriage is then moved in the reverse direction to print another swath of information.
The ink ejecting orifices of an ink jet printer need to be maintained, for example, by periodically cleaning the orifices when the printer is in use, and/or by capping the printhead when the printer is out of use or is idle for extended periods. Capping the printhead is intended to prevent the ink in the printhead from drying out. The cap provides a controlled environment to prevent ink exposed in the nozzles from drying out.
A printhead may also need to be primed before initial use, to ensure that the printhead channels are completely filled with the ink and contain no contaminants or air bubbles. After much printing, and at the discretion of the user, an additional but reduced volume prime may be needed to clear particles or air bubbles which cause visual print defects. Maintenance and/or priming stations for the printheads of various types of ink jet printers are described in, for example, U.S. Pat. No. 4,364,065; 4,855,764; 4,853,717 and 4,746,938, while the removal of gas from the ink reservoir of a printhead during printing is described in U.S. Pat. No. 4,679,059.
The priming operation, which usually involves either forcing or drawing ink through the printhead, can leave drops of ink on the face of the printhead. As a result, ink residue builds up on the printhead face. This ink residue can have a deleterious effect on the print quality. Paper fibers and other foreign material can also collect on the printhead face while printing is in progress. Like the ink residue, this foreign material can also have deleterious effects on print quality. The 717 patent discloses moving a printhead across a wiper blade at the end of a printing operation so that dust and other contaminants are scraped off the orifice before the printhead is capped, and capping the printhead nozzle by moving the printer carriage acting on a sled carrying the printhead cap. This eliminates the need for a separate actuating device for the cap. The 938 patent also discloses providing an ink jet printer with a washing unit which, at the end of the printing operation, directs water at the face of the printhead to clean the printhead before it is capped.